And your script is not always applying CStr() for the number-to-string conversion - although this is probably no big deal.

Bigger problem could be that you might get leading blanks in the string, so you probably need to Trim() as well.
And check if the month format is perhaps 2-digit, like 01 for January, instead of just 1.

It is also a little weird that the & concatenation operators in your script do not have a blank space before and after them, and that your script has both + and & for concatenation operators.

Finally, it may help to concatenate the file paths before executing the fso.CopyFile command (use variables).